The specific aim of this research project is to determine the cellular mechanisms through which the hydroosmotic response of the isolated mammalian collecting tubule occurs during exposure of the tissue to exogenous vasopressin and other naturally occurring hormones. Three major experimental approaches will be utilized. First, the interrelationship between calcium ions, the intracellular binding protein, calmodulin, and the hydroosmotic response to vasopressin will be examined. Modification of medium calcium concentration, the utilization of blockers of cellular calcium uptake, calmodulin inhibition, parathyroid hormone and calcium ionophores will be correlated with the physiologic hydroosmotic response of the isolated rabbit collecting duct to various concentrations of vasopressin and 8-bromo cAMP. Second, studies are planned to explore the physiologic response of the isolated collecting tubule to the presence of other naturally occurring hormones such as somatostatin, kinin, norepinephrine dopamine and thromboxane. In these experiments, the role of cyclic nucleolides, calcium ion, calmodulin and prostaglandin in the hydroosmotic water flow which occurs when the hormones listed above are present, will be examined. Finally, the importance of microfilament and microtubule formation on the hydroosmotic and diffusional water flow mediated by vasopressin will be examined. Drugs such as vinblastine, colchicine, cytochalasin B and phallodin will be used to disrupt microfilament and microtubule formation in the presence and absence of vasopressin, calcium ions and during calmodulin inhibition. These studies should clarify our understanding of the interrelationships of the steps between the binding of these hormones to the collecting duct and the eventual physiologic response which is altered water permeability.